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Epalzeorhynchos bicolor (SMITH, 1931)

Red-Tailed Black Shark

SynonymsTop ↑

Labeo bicolor Smith, 1931


Epalzeorhynchos: From Epalzeo-, which has an unconfirmed derivation and meaning but is often reported incorrectly to denote ‘curative’ (it may actually mean ‘horn’ in reference to a cone-shaped protuberance on the snout of Epalzeorhynchos spp.), and the Ancient Greek ρυνχος (rhynchos), meaning ‘snout, beak’.

bicolor: from the Latin bis-, meaning ‘twice’, and color, meaning ‘colour’, in reference to this species’ distinctive colour pattern.


Order: Cypriniformes Family: Cyprinidae


The species is native to central and western Thailand with historic records from the lower Mae Klong, lower Chao Phraya and Bangpakong rivers, all of which drain into the northern tip of the Gulf of Thailand.

Type locality is ‘Small tributary of Menam Chao Phya River, near Paknampo [Nakorn-Sawan], central Thailand’ and the fish was considered abundant at the time (1931).

It was officially declared extinct in 1996 with collection for the aquarium trade (although there appears to be no evidence to support this), agricultural and domestic pollution, plus other forms of habitat alteration such as dam construction typically considered to blame, but in 2011 a small, highly-localised population was observed in the Chao Phraya basin.

In 2014 it was confirmed to be extant in the Mae Klong system as well, with a single specimen collected from the river’s main channel close to the Maeklong Dam in Muang District, Kanchanaburi Province. Its current status is thus unclear and it is considered critically endangered pending further occurrence records.

All fish traded for ornamental purposes are produced on a commercial basis, probably via the use of hormones.


The specimen recently collected from the Mae Klong was obtained from a flowing stretch of clear water of over a metre in depth, with a substrate of sand and large rocks. Sympatric fish species included Clupeichthys goniognathusNotopterus notopterusRasbora aurotaeniaBarbonymus schwanefeldiiCirrhinus molitorellaOpsarius koratensisMystacoleucus obtusirostrisOsteochilus vittatusO. microcephalusNemacheilus masyaeHomalopteroides smithiAcanthopsoides gracilentus, Pangio oblongaPseudomystus siamensisDermogenys siamensisMastacembelus favusPristolepis fasciata, and Parambassis siamensis.

Other members of the genus tend to be found in flowing rivers and streams and are known to move into temporally-inundated floodplains or forested areas during the wet season. It is these migratory patterns that are thought to have been disrupted by human development.

Maximum Standard Length

100 – 125 mm.

Aquarium SizeTop ↑

An aquarium with base measurements of 120 ∗ 45 cm should be the smallest considered, with larger quarters necessary for a group.


Provided sufficient cover is available this species is relatively unfussy in terms of décor, and should not harm softer-leaved plants. However it will thrive in a set-up designed to resemble a flowing river with a substrate of variably-sized rocks, gravel and some larger, water-worn boulders.

This can be further furnished with driftwood roots and branches plus aquatic plants from genera such as Microsorum, Bolbitis or Anubias which can be grown attached to the décor. Bright lighting will promote the growth of algae and associated microorganisms, upon which the fish will graze.

Like many fishes that naturally inhabit running water it’s quite intolerant to the accumulation of organic wastes and does best if there is a high level of dissolved oxygen and moderate water movement.

Water Conditions

Temperature20 – 26 °C

pH: Happy within the range 6.0 – 8.0 but a value close to neutral is usually recommended.

Hardness36 – 268 ppm


Primarily an aufwuchs grazer feeding on algae, small crustaceans, insect larvae, etc., and for it to develop its best colours and condition it should be offered regular meals of small live and frozen foods such as chironomid larvae (bloodworm), Daphnia and Artemia along with good quality dried flakes, granules and fresh plant material.

Shelled peas, cucumber, blanched courgette, spinach and chopped fruit all make good additions to the menu. Once settled it will often ascend into midwater to feed and browse the biofilm that tends to form on rockwork and other solid surfaces.

Behaviour and CompatibilityTop ↑

Though normally sold as such this species is largely unsuitable for the general community aquarium. This does not mean to say it must be kept alone, rather that tankmates must be chosen with care. While small specimens tend to hide away much of the time they become increasingly territorial as they grow and can display particularly high levels of aggression towards similar-looking species.

Some individuals are more belligerent than others and there exist reports of apparent alliances with other species such as Chromobotia macracanthus. We’re unsure if these behavioural differences are indicative of gender but at any rate loaches from the genera Chromobotia, Botia, Syncrossus and Yasuhikotakia do seem to be left in peace by Epalzeorhynchos species whereas congenerics and members of Crossocheilus, Garra and Gyrinocheilus, for example, tend to be attacked constantly. Please note that in terms of the loaches not all may be housed together and proper research is essential.

Other bottom-dwelling fishes including cichlids and most catfish are best avoided as they may too be picked on. For the upper levels choose robust, active, schooling cyprinids. Ideally the Epalzeorhynchos should be the final addition to the tank in order to avoid it claiming ownership of the entire space.

This species probably lives a solitary lifestyle and in nature would probably have only come into contact with others of its own kind infrequently and during the spawning season. These instincts heighten as the fish get older and we therefore recommend it be kept singly in the majority of cases. In a very large tank with lots of cover a cohabitation attempt might be possible but each individual is likely to require a territory with a diameter of at least a metre.

Sexual Dimorphism

Sexually mature females are noticeably thicker-bodied than males but it’s impossible to sex young specimens accurately by external means. It’s possible that males develop slightly longer unpaired fins.


As far as we know it has not been bred in private aquaria. Large numbers are produced on commercial farms via the artificial use of hormones.

NotesTop ↑

Despite its popularity as an aquarium fish this species is rarely maintained in ideal conditions. Juveniles are typically being offered for sale with little to no information regarding temperament, eventual size, and potential age in excess of 15 years.

It is also often sold as an algae-eater and while it does browse on algae it does not do so with the same efficacy as some Crossocheilus species, for example, and there’s little worth in purchasing it with that purpose in mind.

Most members of Epalzeorhynchos were formerly regarded as Labeo spp. and are thus referred to as such in older literature. According to Rainboth (1996) they are characterised by absence of a dorsal spine, possession of 10-13 branched dorsal fin rays, a thin membrane connecting the upper and lower lips and rigid, freely moveable rostral lobes.

Epalzeorhynchos itself has undergone some quite recent changes with a handful of species having been reassigned to Crossocheilus and E. bicornis moved to the new genus Akrokolioplax (Zhang and Kottelat, 2006). The latter was erected on the basis of differences in oral morphology and the position/structure of the so-called ‘rostral lateral lobes’ on the snout, a feature unique to these two genera.

Of the remaining species E. frenatum and E. kalopterus have been mainstays of the aquarium hobby for many years while the identity of E. munense now appears established. Smith (1934) described it as possessing a brown body, black dorsal fin edged in white and a white caudal fin, with type locality given as the Mun/Moon river, a tributary of the Mekong in eastern Thailand.

Fish collected since are similar in appearance to E. bicolor and E. frenatum, but distinguishable by a unique combination of black head, body and anal-fin, red caudal and dorsal fins, and black margins on the pelvic and pectoral fins (Kottelat, 1998).

These features have been recognised by several authors who also noted that preserved specimens tended to lose the red pigmentation in the fins after three months in alcohol and that the holotype of E. munense had been collected eight years prior to its description, thus live colouration was not included. The possibility that E. frenatum and E. munense have hybridised in aquaculture at some point cannot be discounted.

Some SF forum members keep/have kept a fish which closely resembles E. bicolor but possesses a white caudal fin and is most often found among batches of E. frenatum. It is unclear whether this is a genetic sport among farm-bred fish or a potentially undescribed species but certainly the white pigmentation does not alter with age or conditioning.

There is also a commercially-produced anerythristic (lacking red pigment) mutation of E. frenatum that has pale yellowish fins and has sometimes been misidentified as E. munense. A recent introduction to the hobby is an albino form of E. bicolor but this has yet to achieve the same degree of popularity as the ubiquitous albino E. frenatum.


  1. Smith, H. M., 1831 - Proceedings of the United States National Museum 79(2873): 1-48
    Descriptions of new genera and species of Siamese fishes.
  2. Kulabtong, S., S. Suksri, C. Nonpayom, and Y. Soonthornkit, 2014 - Biodiversity Journal 5(2): 371-373
    Rediscovery of the critically endangered cyprinid fish Epalzeorhynchos bicolor (Smith, 1931) from West Thailand (Cypriniformes: Cyprinidae).
  3. Kottelat, M., 1998 - Ichthyological Exploration of Freshwaters 9(1): 1-128
    Fishes of the Nam Theun and Xe Bangfai basins, Laos, with diagnoses of twenty-two new species (Teleostei: Cyprinidae, Balitoridae, Cobitidae, Coiidae and Odontobutidae).
  4. Kottelat, M., 2013 - The Raffles Bulletin of Zoology Supplement 27: 1-663
    The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.
  5. Rainboth, W. J., 1996 - FAO, Rome: 1-265
    Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes.
  6. Yang, J.-X. and R. Winterbottom , 1998 - Copeia 1998(1): 48-63
    Phylogeny and zoogeography of the cyprinid genus Epalzeorhynchos Bleeker (Cyprinidae: Ostariophysi).
  7. Zhang, E. and M. Kottelat, 2006 - Zootaxa 1225: 21-30
    Akrokolioplax, a new genus of Southeast Asian labeonine fishes (Telesotei: Cyprinidae).

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